I love summer days spent outside with my dog, Bravo, but mosquito bites drive us both buggy. They're a danger to my cat, Karma, too, even though he rarely goes outside for leash walks. These tiny vampires are more than an itchy aggravation. Mosquito bites spread heartworms and can kill cats and dogs. The highest risk is found in warm climates where mosquitoes thrive. Southeastern states, the Mississippi River Valley, and Texas pose the highest risk, but heartworm disease is found in all 50 states. (That's why it's so important to check the parasite forecast in your area.) Here's what you need to know about mosquito bites and your pets.
Canine Heartworm Disease
Dogs are the natural host—the disease even affects coyotes and wolves—but cats also get heartworms. Heartworm disease is caused by a type of roundworm, a parasite more technically called a filarid. The heartworm lifecycle takes about seven months. When a mosquito bites an already infected dog, it swallows the immature parasite, called microfilariae. While inside the mosquito, these baby heartworms continue to develop. When the mosquito bites again, it leaves behind the larvae, which infect the new dog through the mosquito bite wound. The immature heartworms go through many stages inside the pet's body and ultimately end up in the heart and lungs. A dog's heart may hold dozens of worms that are four- to twelve-inches long. The adult worms reproduce to complete the life cycle. A single worm can shed 5,000 microfilariae a day into the bloodstream. Heartworms damage the heart and ultimately causes congestive heart failure.
Feline Heartworm Disease
Cats are known as "dead-end hosts." Their small heart usually can't contain enough adult worms to be able to reproduce. To become infected, a cat must live in an area with infected dogs and with mosquitoes that have a taste for both dog and cat blood. The Companion Animal Parasite Council reports cat heartworm disease incidence at about 10 to 15 percent that of dogs in any geographic location. While dogs may live with dozens of worms for years before they show symptoms, one worm can make your cat very sick and two worms can kill.
Signs of Heartworm Disease
Even though it's the same disease, the symptoms, diagnosis and treatment are different for dogs and cats. In dogs, heartworm disease is a chronic condition in which worms live in the dog for up to five years. Dogs may not show symptoms at first, but problems get worse over time. Left untreated, the dog may collapse and die. Chronic symptoms include coughing, shortness of breath, reluctance to exercise, fainting after exertion, weakness, weight loss, and coughing up blood.
Cats with heartworms suffer from diseases of the arteries of the lungs. Coughing, which is rare in cats, is one common sign of feline heartworm disease. The acute form of the disease occurs frequently. Cats appear normal one moment, then suffer sudden respiratory failure and die within minutes. The American Heartworm Society includes these cat heartworm symptoms: difficulty breathing, wheezing and coughing, unexplained vomiting, and can lead to sudden death.
Diagnosing and Treating Heartworm Disease
Diagnosis is based on signs of disease, blood-screening tests, and sometimes X-rays and echocardiography. Traditional tests look for microfilariae in blood samples, but this isn't helpful in cats that rarely have immature worms. Veterinarians use melarsomine, a drug related to arsenic, to kill the adult worms in dogs. Additional treatment takes care of the immature stages of the parasite. Enforced rest during treatment is vital to avoid deadly complications when the worms die and can cause blockages. Treating dogs can be expensive, and hard on the dog. There's no safe treatment for cats. Because the adult worms live in the pulmonary arteries, killing them can block the blood flow in the cat's lungs. This embolism can kill the cat.
Preventing Mosquito Bites and Heartworm Disease
It is much easier and less expensive to prevent heartworm disease than to diagnose, treat, and cure it once infection is present. Keeping pets indoors during mosquito feeding times, like late afternoons and evenings, will help. Frequently clean bird baths or eliminate standing water to prevent mosquito breeding. Some flea prevention products also shoo away mosquitoes. Veterinarians recommend year-round prescription medications available as pills, spot-on, or injectable products that stop the disease even if your pet suffers mosquito bites. Some combination products also prevent other parasites like fleas or ticks and are every effective and safe.